Maybe a different blends of UV light, like there's one for aquariums that are mostly plastic or rock, there's one that gives off UV for land critters and (i think) one for reptiles with differing light requirements, such as a Bearded Dragon (Desert daylight hunter) and turtles...it would be quite expensive, since UV bulbs aren't cheap, but does yours (the one you use presently) fade the ponies faster than in sunlight? Maybe even having a UV blacklight would help...hmm.